The techniques for informing a driver of “audio information useful for driving” with the use of “speech guidance (such as speech guidance for informing a person of the presence of a pedestrian in a vehicle moving direction, speech guidance for informing a person of the presence of a car at a change destination when changing driving lanes, speech guidance for informing a person of the possibility of a guide word to be appeared on a driving lane, and speech guidance for a car navigation)” has been recently known.
However, judging or comprehending “information” by listening to “speech guidance” gets difficult due to a variety of “speech guidance.”
Therefore, the technique for combining “speech guidance” and a “warning sound (i.e., a sound different from speech guidance such as a chime sound or a buzzing sound)” has been proposed (see Patent Document 1).